We propose to study biogenetic relations and functional interactions among the membranes of those intracellular compartments that together constitute the secretory pathway (or the endoplasmic reticulum-plasmalemma pathway). These compartments include the endoplasmic reticulum, a series of Golgi compartments, secretory vacuoles (or granules) and different carrier vesicles active at different junctions along this pathway which leads to discharge sites on the plasmalemma. Whenever needed, we propose to improve cell fractionation procedures by using specific ligands (e.g. antibodies or lectins) - rather than general physical properties - for the isolation of subcellular components. The cell fractions obtained will be used to isolate and purify their membranes. The proteins of these membranes will be analyzed and identified by appropriate procedures e.g., gel electrophoresis, immuneoverlays, immunoprecipitation, other biochemically specific interactions, that can be carried out on gels or gel transfers. The cell types selected for systematic investigation are the murine erythroblasts (normal or transformed) and the rat hepatocyte. The membrane proteins of primary interest are: 1) the murine glycophorins (for erythroblasts) and 2) the secretory component (for hepatocyte). Other membrane proteins will be selected in time. In each case, the pathway followed by these proteins from their sites of synthesis to their sites of final functional residence (or discharge) will be followed and the compartments involved in each postranslocational modification will be identified. With this information secured, attempts will be made to analyze the mechanisms involved in the control of intracellular vesicular traffic and - in conjunction with it - in the control of chemical specificity among interacting membranes.